It is desirable that local affiliate stations of a television network be able to incorporate their own call letters or logos with network advertisements of upcoming network programming (commonly referred to as "promos") so that television viewers will associate their favorite programs with the local affiliate. Hereinafter this type of function will be called "station signature".
One way of accomplishing station signature would be for the local station to continuously monitor the network promo and switch in a video overlay of his call letters and/or logo at the appropriate time. The video overlay can be generated by a selectively actuated telecine camera or a character generator which is operated synchronously (genlocked) with the program material for switching in the local information. However, this technique is expensive in terms of manpower and equipment, both of which can be put to a more productive use by the local station. Therefore, it would be desirable for station signature to be done automatically.
It is known in the prior art to insert auxiliary signals into the horizontal and/or vertical blanking intervals of a transmitted television signal for transmitting information, such as closed-captioning, teletext, color control signals, etc. However, the inclusion of an auxiliary signal for automatic station signature, which will hereinafter be referred to as a "trigger" signal, in the blanking interval of a television signal is incompatible with present studio tape recording machines. This is so because the studio tape machines used for making a duplicate tape a dub, delete the blanking signals of the source material and insert new blanking signals into the dub. Thus, blanking interval triggers would be removed from the program source material as a result of dubbing and therefore are inappropriate triggers for accomplishing automatic station signature.
Furthermore, it is known for the network to transmit a signal for causing a flashing white box (commonly called a "net cue") to appear within the upper right-hand corner of the active portion of the television picture to indicate a commercial message is about to be sent. The net cue is not visible to television viewers since it is positioned to appear in the raster edge overscan which is conventional in television receivers. At the local stations a monitor, which reproduces the full raster, is used to allow visual detection of the net cue for determining the proper time to initiate insertion of local information. While an electronic detector could be used to sense the white box signal of the net cue for automatically generating a signal to control the insertion of local information, scene content of the program may erroneously cause an indication of the presence of a net cue has been sensed and result in inappropriate operation of the station signature system, thereby jeopardizing the integrity of the television program material. Furthermore, due to last minute scheduling changes that are inherent in network programming (due to, for example, special events such as news bulletins or extra time needed for a sporting event), insertion of the net cue at the network is performed manually and therefore places an extra burden on network personnel and equipment at air time. For this and the other above-noted reasons, a net cue is an inappropriate type of trigger for automatic station signature over prerecorded material.
Thus, it is desirable to provide a station signature system for prerecorded material, i.e., promos, which includes a trigger signal which is not lost if the source material is dubbed and which can be automatically and reliably sensed by monitoring equipment at the local station.